Top: Throughput of the three broad-band NIRISS filters used in this analysis: F115W, F150W, and F200W. The shaded regions correspond to the wavelength range within which the throughput is greater than 50% of the peak value. Bottom: Visibility of a selection of strong optical-NIR emission lines (solid lines) and absorption features (dot-dashed lines), varying with redshift. On the left of the plot, we show the approximate redshift ranges in which multiple strong lines are visible. The cluster redshift (z = 0.3064) is denoted by the dashed line.